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A potassium salt of the N2S2O2-coordination Fe(III) anion K[Fe(5Cl-thsa)2] (1) (5Cl-thsa - 5-chlorosalicylaldehyde thiosemicarbazone) is synthesized and characterized structurally and magnetically over a wide temperature range. Two polymorphs of salt 1 characterized by the common 2D polymer nature and assigned to the same orthorhombic Pbcn space group have been identified. The molecular structure of the minor polymorph of 1 was solved and refined at 100, 250, and 300 K is shown to correspond to the LS configuration. The dominant polymorph of 1 features K+ cations disordered over a few crystallographic sites, while the minor polymorph includes fully ordered K+ cations. The major polymorph exhibits a complete three-step cooperative spin-crossover transition both in the heating and cooling modes: The first step occurs in a temperature range from 2 to 50 K; the second abrupt hysteretic step occurs from 200 to 250 K with T1/2 = 230 K and a 6 K hysteresis loop. The third gradual step occurs from 250 to 440 K. According to 57Fe Mossbauer, XRPD, and EXAFS data, the spin-crossover transition for the dominant polymorph is quite peculiar. Indeed, the increase in the HS concentration by 57% at the second step does not result in the expected significant increase in the iron(III)-ligand bond lengths. In addition, the final step of the spin conversion (ΔγHS = 26%) is associated with a structural phase transition with a symmetry lowering from the orthorhombic (Pbcn) to the monoclinic (P21/n) space group. This nontrivial phenomenon was investigated in detail by applying magnetization measurements, electron spin resonance, 57Fe Mossbauer spectroscopy, and DFT calculations. These results provide a new platform for understanding the multistep spin-crossover character in the Fe(III) thsa-complexes and related compounds.

Layered oxyhalides containing double or triple fluorite layers are promising visible-light-responsive water-splitting photocatalysts with unique band structures. Herein, we report on the synthesis, structure, and photocatalytic property of Bi4BaO6Cl2 (I4/mmm) with alternating double (Bi2O2) and triple (Bi2BaO4) fluorite layers, which was extracted from the crystallographic database on the basis of Madelung potential calculations. Rietveld refinements from powder X-ray and neutron diffraction data revealed the presence of cationic disorder between Bi2O2 and Bi2BaO4 layers, leading to electrostatic stabilization. DFT calculations suggested that photogenerated electrons and holes flow through the double and triple layers, respectively, which may suppress electron-hole recombination. We expanded this double-triple system to include Bi4CaO6Cl2 and Bi4SrO6Cl2 with orthorhombic distortions and different degrees of cationic disorder, which allow band gap tuning. All the double-triple compounds Bi4AO6Cl2 showed stable water-splitting photocatalysis in the presence of a sacrificial reagent.

The quaternary selenide Ba4GeSb2Se11 was prepared by a high-temperature solid state reaction method. Ba4GeSb2Se11 crystallizes in an acentric orthorhombic space group Cmc21 with the lattice constants a = 9.370(11) A, b = 25.850(0) A, and c = 8.798(10) A. The compound is composed of a [SbSe3]3- trigonal pyramid, [GeSbSe5]3- dimers, V-shaped Se32-, and the adjacent Ba2+ ions. It has indirect band gap of 1.35 eV and exhibits a second harmonic generation intensity of about 0.2 times that of the benchmark compound AgGaS2 at the same particle size. Interestingly, theoretical analyses show that the central Se atom of Se32- has the largest contribution (8.1%) to d31 compared to that of other Se atoms, which may be due to its easy swing in the a-axis direction.

We provide the material synthesis method, crystal structure information, and characterization of a novel mixed-valent metal oxide KIn0.33IIITe0.67VITe2IVO7, closely related to zirconolite (CaZrTi2O7), a radioactive waste immobilized material, having a 3D framework. The reported metal oxide containing an alkali-metal cation (K+), main-group cation (In3+), tellurate, and tellurite has been synthesized as both single crystals and a pure polycrystalline phase through a hydrothermal synthesis method. Single-crystal X-ray diffraction indicates that KIn0.33Te2.67O7 crystallizing in the orthorhombic space group Cmcm (No. 63) reveals a 3D framework structure with a 1D channel consisting of Te/InO6 octahedra and TeO4 polyhedra. An interesting transition reaction from KIn0.33Te2.67O7 to KIn(TeO3)2 under hydrothermal conditions at 230 °C is discussed.

Two alkali tin(II) phosphates, namely, Rb[SnF(HPO4)] and Rb(Sn3O)2(PO4)3, were synthesized through mild hydrothermal methods. They belong to the orthorhombic Pnma and Pbcn space groups, respectively. Rb[SnF(HPO4)] features a layered structure based on 1D [SnF(HPO4)]∞ chains interconnected by hydrogen bonds, with Rb+ cations located at the interlayer space. For Rb(Sn3O)2(PO4)3, each pair of [Sn3O]4+ clusters is bridged by a pair of [P(1)O4]3- tetrahedra to build a 1D [Sn-P-O]∞ chain. These 1D [Sn-P-O]∞ chains are further cross-linked though [P(2)O4]3- tetrahedra to construct a 3D network with 7- and 10-membered-ring channels. The tin(II) ions in Rb[SnF(HPO4)] and Rb(Sn3O)2(PO4)3 with stereochemically active lone pairs (SCALPs) significantly enhance the birefringences of metal phosphates: Δn = 0.147@1064 nm for Rb[SnF(HPO4)] and 0.082@1064 nm for Rb(Sn3O)2(PO4)3.

Demands for IR birefringent materials are increasing due to the rapid developments of IR laser applications. Herein, two new chain tellurides β-BaGa2Te4 and Ba5Ga2Ge3Te12 have been discovered. β-BaGa2Te4 crystallizes in the orthorhombic space group Imma (no. 74) with unit cell constants of a = 23.813(3) A, b = 11.9673(19) A, and c = 6.7215(9) A, while Ba5Ga2Ge3Te12 crystallizes in the monoclinic space group P21/c (no. 14) with unit cell constants of a = 13.6540(3) A, b = 9.6705(2) A, and c = 23.1134(7) A. The structure of β-BaGa2Te4 can be considered to be the antiparallel arrangement of one-dimensional (1D) [GaTe2] chains formed by edge-sharing GaTe4 tetrahedra, which are separated by Ba2+ cations. In the crystal structure of Ba5Ga2Ge3Te12, two kinds of 1D chains, namely chain 1 ∞1[(GaGe)3Te8] and chain 2 ∞1[(GaGe)2Te4], are stacked alternately and put together by the coulomb force with Ba2+ cations. In addition, First-principles calculations indicate that β-BaGa2Te4 has a large birefringence, ∼0.325 at 2050 nm, derived from the superposition of the polarizabilities of GaTe4 tetrahedra, implying that it has potential as an IR birefringent material. This work may provide some guidance for exploring new IR birefringent crystals.

A new alkali metal-rare earth metal anhydrous sulfate, KTb(SO4)2 (KTSO), was synthesized by a hydrothermal method. It crystallized in the non-centrosymmetric (NCS) orthorhombic space group P212121 with cell parameters a = 5.43950(10), b = 8.8579(3), c = 13.3962(4), Z = 2. Its structure is composed of [KO11], [TbO8], and [SO4] groups, which are interconnected to constitute a one-dimensional (1D) chain, and then further linked to construct a three-dimensional (3D) network structure through [SO4] units. The results of the powder frequency doubling test show that KTb(SO4)2 has a phase-matching second-order nonlinear optical effect of 0.3 times that of KH2PO4 (KDP). The measured birefringence of the crystal (0.01) agrees well with the calculated value (0.019). Meanwhile, its infrared and ultraviolet spectrum and thermal properties were studied, respectively. Its optical properties and band gap structure are studied by theoretical calculation. This work provides a NCS structure of anhydrous sulfates and offers guidance for further exploration of new anhydrous sulfates.

We have synthesized the orthocarbonate Sr3[CO4]O in a laser-heated diamond anvil cell at 20 and 30 GPa by heating to ≈3000 (300) K. Afterward, we recovered the orthocarbonate with [CO4]4- groups at ambient conditions. Single-crystal diffraction shows the presence of [CO4]4- groups, i.e., sp3-hybridized carbon tetrahedrally coordinated by covalently bound oxygen atoms. The [CO4]4- tetrahedra are located in a cage formed by corner-sharing OSr6 octahedra, i.e., octahedra with oxygen as a central ion, forming an antiperovskite-type structure. At high pressures, the octahedra are nearly ideal and slightly rotated. The high-pressure phase is tetragonal (I4/mcm). Upon pressure release, there is a phase transition with a symmetry lowering to an orthorhombic phase (Pnma), where the octahedra tilt and deform slightly.

The novel α-BaZn2P2 structural polymorph has been synthesized and structurally characterized for the first time. Its structure, elucidated from single crystal X-ray diffraction, indicates that the compound crystallizes in the orthorhombic α-BaCu2S2 structure type, with unit cell parameters a = 9.7567(14) A, b = 4.1266(6) A, and c = 10.6000(15) A. With β-BaZn2P2 being previously identified as belonging to the ThCr2Si2 family and with the precedent of structural phase transitions between the α-BaCu2S2 type and the ThCr2Si2 type, the potential for the pattern to be extended to the two different structural forms of BaZn2P2 was explored. Thermal analysis suggests that a first-order phase transition occurs at ∼1123 K, whereby the low-temperature orthorhombic α-phase transforms to a high-temperature tetragonal β-BaZn2P2, the structure of which was also studied and confirmed by single-crystal X-ray diffraction. Preliminary transport properties and band structure calculations indicate that α-BaZn2P2 is a p-type, narrow-gap semiconductor with a direct bandgap of 0.5 eV, which is an order of magnitude lower than the calculated indirect bandgap for the β-BaZn2P2 phase. The Seebeck coefficient, S(T), for the material increases steadily from the room temperature value of 119 μV/K to 184 μV/K at 600 K. The electrical resistivity (ρ) of α-BaZn2P2 is relatively high, on the order of 40 mΩ·cm, and the ρ(T) dependence shows gradual decrease upon heating. Such behavior is comparable to those of the typical semimetals or degenerate semiconductors.

We synthesized single crystals of marokite (CaMn2O4)-type orthorhombic manganese (II,III) oxide, γ-Mn3O4, in a multianvil apparatus at pressures of 10-24 GPa. The magnetic, electronic, and optical properties of the crystals were investigated at ambient pressure. It was found that γ-Mn3O4 is a semiconductor with an indirect band gap Eg of 0.96 eV and two antiferromagnetic transitions (TN) at ∼200 and ∼55 K. The phase stability of the γ-Mn3O4 crystals was examined in the pressure range of 0-60 GPa using single-crystal X-ray diffraction and Raman spectroscopy. A bulk modulus of γ-Mn3O4 was determined to be B0 = 235.3(2) GPa with B' = 2.6(6). The γ-Mn3O4 phase persisted over the whole pressure range studied and did not transform or decompose upon laser heating of the sample to ∼3500 K at 60 GPa. This result seems surprising, given the high-pressure structural diversity of iron oxides with similar stoichiometries. With an increase in pressure, the degree of distortion of MnO6 polyhedra decreased. Furthermore, there are signs indicating a limited charge transfer between the Mn3+ ions in the octahedra and the Mn2+ ions in the trigonal prisms. Our results demonstrate that the high-pressure behavior of the structural, electronic, and chemical properties of manganese oxides strongly differs from that of iron oxides with similar stoichiometries.

Three new alkali-metal manganese fluoride selenates, A2Mn(SeO4)F3 (A = K, Rb, Cs), were prepared through hydrothermal redox reactions. The products consisted of one-dimensional polymeric anionic ∞[Mn(SeO4)F3]2- chains, where the A+ cations are connected by O and/or F atoms to form blocks with two-dimensional layers. A2Mn(SeO4)F3 (A= Rb, Cs) is isostructural with the monoclinic space group P21/c, while K2Mn(SeO4)F3 crystallizes in the orthorhombic space group Pbcn. A2Mn(SeO4)F3 (A = K, Rb, Cs) forms spin chains of Mn3+ with different Mn-F-Mn bridges, which showed canting antiferromagnetic behaviors. Single-crystal magnetic measurements revealed that the magnetic moments of the Mn ions were more canted for larger alkali-metal compounds in an antiferromagnetically ordered state.

International audience; SrREGa3O7 melilite ceramics with large rare-earth elements (RE = La to Y) are famous materials especially known for their luminescence properties. Using an innovative approach, the full and congruent crystallization from glass process, SrREGa3O7 transparent polycrystalline ceramics with small rare earth elements (RE = Dy-Lu and Y) have been successfully synthesized and characterized. Interestingly, compared to the classic tetragonal (P-421m) melilite structure composed of mixed Sr/RE cationic sites, these compositions can crystallize in a 3 x 1 x 1 orthorhombic (P21212) superstructure. A detailed study of the superstructure, investigated by different techniques (synchrotron and neutron powder diffraction, STEM-HAADF imaging and EDS mapping), highlights the existence of a Sr/RE cation ordering favored by a large Sr/RE size mismatch and a sufficiently small RE cation. An appropriate control of the synthesis conditions through glass crystallization enables the formation of the desired polymorphs, either ordered or disordered. The influence of this tailored cationic ordering/disordering on the RE luminescent spectroscopic properties have been investigated. A stronger structuration of the RE emission band is observed in the ordered ceramic compared to the disordered ceramic and the glass, whose band shapes are very similar, indicating that the RE environment in the glass and disordered ceramic are close.

Two triclinic A2ZnSi3S8 (A = Rb and Cs) with layered structures were successfully synthesized, and their physicochemical performances including optical bandgap, thermal behavior, and optical anisotropy were investigated. A2ZnSi3S8 could be viewed as the first discovered Si-based examples in the known A2MIIMIV3Q8 family (2-1-3-8 system; A = monovalent alkali metal; MII = divalent transition metal; MIV = group 14 metal; Q = chalcogen). The A2MIIMIV3Q8 family members crystallize in five different space groups (P1, P21, P21/n, P212121, and Pa3), and their structural transformation and optical performances (bandgap, NLO coefficient, and birefringence) were systematically studied based on the first-principles calculation among 13 A2MIIBMIV3Q8 (MIIB = Zn, Cd, and Hg) compounds without cubic β-K2ZnSn3S8. Research result shows that the above 13 compounds exhibit the layered structures, but diverse wavelike layers and their optical anisotropy (Δn) undergo an increasing trend range from the triclinic to orthorhombic systems. Moreover, P212121 compounds have very weak NLO effects compared with those of the P21 compounds since the polarization directions of anionic groups (MIIBQ4 and MIVQ4) in P212121 compounds are directing oppositely and almost completely canceled out by the dipole moment calculation, which further indicates that P21 compounds exhibiting the relatively strong NLO effect and large optical anisotropy could be expected as potential IR NLO candidates.

Quaternary nonlinear optical single crystals AgxGaxGe1-xSe2 (x = 0.250, 0.167) were grown by the Bridgman method in a four-zone furnace. The thermal expansion behavior of AgxGaxGe1-xSe2 (x = 0.25, 0.167) was studied by the method of single-crystal X-ray diffraction from 150 to 295 K and powder X-ray diffraction in the range of 298-773 K. Both results show the crystals have positive linear thermal expansion coefficients in different directions and a positive volume thermal expansion coefficient, and it is observed that they satisfy the relationship of αa > αc > αb and αV ≈ αa + αb + αc for the orthorhombic structure. It is found that the AgxGaxGe1-xSe2 (x = 0.25, 0.167) unit cells varying with temperature were mainly dominated by variations in framework geometry (AgSe4 tetrahedron), and the thermal motion of Ag atoms in the AgSe4 tetrahedron. As it was revealed, according to the powder X-ray diffraction, it is found that the isotropic thermal atomic displacement parameter of the Ag atoms is much larger than those of the Se and Ga(Ge) atoms in the AgSe4 tetrahedron. Furthermore, anisotropic atomic displacement parameters (ADPs) of Ag atoms are extracted from the single-crystal diffraction; the ADPs along the a axis, b axis, and c axis have a significant difference, which means the thermal vibration of Ag atoms is anisotropic. It is of great significance for improving crystal growth technology and understanding the thermal properties of this kind of crystals.

The influence of different synthesis routes on the structure and luminescent properties of KTb(MoO4)2 (KTMO) was studied. KTMO samples were prepared by solid-state, hydrothermal, and Czochralski techniques. These methods lead to the following different crystal structures: a triclinic scheelite-type α-phase is the result for the solid-state method, and an orthorhombic KY(MoO4)2-type γ-phase is the result for the hydrothermal and Czochralski techniques. The triclinic α-KTMO phase transforms into the orthorhombic γ-phase when heated at 1273 K above the melting point, while KTMO prepared by the hydrothermal method does not show phase transitions. The influence of treatment conditions on the average crystallite size of orthorhombic KTMO was revealed by X-ray diffraction line broadening measurements. The electrical conductivity was measured on KTMO single crystals. The orthorhombic structure of KTMO that was prepared by the hydrothermal method was refined using synchrotron powder X-ray diffraction data. K+ cations are located in extensive two-dimensional channels along the c-axis and the a-axis. The possibility of K+ migration inside these channels was confirmed by electrical conductivity measurements, where strong anisotropy was observed in different crystallographic directions. The evolution of luminescent properties as a result of synthesis routes and heating and cooling conditions was studied and compared with data for the average crystallite size calculation and the grain size determination. All samples' emission spectra exhibit a strong green emission at 545 nm due to the 5D4 → 7F5 Tb3+ transition. The maximum of the integral intensity emission for the 5D4 → 7F5 emission under λex = 380 nm excitation was found for the KTMO crashed single crystal.

A novel modification of the KCoPO4, δ-phase has been prepared by hydrothermal synthesis at 553 K. The compound crystallizes in the orthorhombic system with the unit-cell parameters a = 8.5031(8), b = 10.2830(5), c = 54.170(4) A. The crystal structure was determined based on synchrotron low-temperature single-crystal X-ray diffraction data obtained from an inversion twin in the space group P212121 and refined to R = 0.077 for 5156 reflections with I > 3σ(I). The δ-KCoPO4 possesses a new structure type which is based on a framework built from sharing vertices Co- and P-centered tetrahedra. The {CoPO4-}∞ construction of tetrahedra may be described as assembled from networks formed by two topologically diverse six-membered rings of tetrahedra stacked together through vertex-bridging contacts along the a axis. The ratio of the (UUUDDD) and (UUDUDD) rings, where (U) and (D) denote the orientation of the tetrahedra in the six-membered rings up and down relative to the plane grids, is equal to 5:1. The (UUDUDD) rings form bands parallel to the [010] direction each surrounded from both sides along the c axis by slabs of five ribbons width having alternative (UUUDDD) topology. Open in the [100] direction channels incorporate K+ ions; this structural feature permits to suppose ion-conductive and/or electrochemical properties of the title compound. The possible mechanism of the δ → γ phase transition is discussed on the basis of the crystal chemical analysis of the KCoPO4 polymorphs. The title compound orders magnetically at TN = 24.8 K.

The ternary Zn-Sb oxide β-Zn7Sb2O12 was prepared by solid state synthesis from ZnO and Sb2O3 at 1250 °C and a reaction time of 168 h. The crystal structure of β-Zn7Sb2O12 was solved from powder diffraction data by direct-space methods and was refined by the Rietveld technique. The title compound β-Zn7Sb2O12 crystallizes in the orthorhombic space group Cmme with a = 1210.6(1) pm, b = 1856.7(1) pm, c = 852.2(1) pm, V = 1.9154(1) nm3, and eight formula units per unit cell. The structure can be described as a distorted cubic closest packing of oxide ions with Zn2+ and Sb5+ in the tetrahedral and octahedral interstitial sites. According to group-subgroup relations, the anion packing is directly derived from the spinel structure of α-Zn7Sb2O12; however, the occupation pattern of the interstitials is completely different than in the spinel structure type. The most prominent structural feature in β-Zn7Sb2O12 is the clustering of all [ZnO4] polyhedra into a [Zn7O20] moiety representing an excerpt from the sphalerite structure. The structural model is corroborated by vibrational spectroscopy as well as density functional theory calculations. Thermal analysis reveals an irreversible phase transition of β-Zn7Sb2O12 into the α-polymorph at 1330 °C.

The discovery of the (Li1-xFexOH)FeSe superconductor has aroused significant interest in metal hydroxide-intercalated iron chalcogenides. However, all efforts made to intercalate NaOH between FeSe and FeS layers have failed so far. Here we report two NaOH-intercalated iron chalcogenides (Na1-xOH)Fe1-yX (X = Se, S) that were synthesized by a low-temperature hydrothermal ion-exchange method. Their crystal structures were solved through single-crystal X-ray diffraction and refined against powder X-ray and neutron diffraction data. Different from the (Li1-xFexOH)FeX superconductors that crystallize in a tetragonal space group P4/nmm with Z = 2, (Na1-xOH)Fe1-yX belong to an orthorhombic space group Cmma with Z = 4. The structural solution also reveals that there are vacancies in both Na and Fe sites and there are not iron ions in the (Na1-xOH) layer. This is probably why both Fe(II) and Fe(III) species exist in the title compounds, as detected by X-ray photoelectron spectroscopy. Based on magnetization and electrical resistivity measurements, the two compounds were found to be paramagnetic semiconductors. The absence of superconductivity should be closely related to the iron vacancies in the Fe1-yX layer. Theoretical calculations suggest that inducing superconductivity in (Na1-xOH)Fe1-ySe is promising due to the similarity of the electronic structures between stoichiometric (NaOH)FeSe and the (Li1-xFexOH)FeSe superconductor.

We report the synthesis, single-crystal structure, solid-state ultraviolet-visible-near-infrared spectroscopy, and theoretical calculations on the first trivalent plutonium crown ether inclusion complex, [(H3O)(18-crown-6)][Pu(H2O)4(18-crown-6)](ClO4)4·2(H2O) (denoted as PuIII-18C6). Single-crystal X-ray diffraction reveals that PuIII-18C6 crystallizes in the orthorhombic space group of Pccn, which is assembled by independent ionic pairs including [Pu(H2O)4(18-crown-6)]3+, [(H3O)(18-crown-6)]+, and perchlorate anions. The plutonium atom is fully encapsulated within the cavity of the 18-crown-6, generating a distorted bicapped square antiprism geometry. The theoretical evaluation confirms that weak Pu-O dative bond is involved between PuIII ions with 18-crown-6. This work may deepen the understanding of the host-guest interactions between trivalent transuranic and macrocyclic ligands.

Crystals of two strontium niobium oxyfluorides, Sr2Nb6O13F8·4H2O and Sr3Nb2O2F12·2H2O, have been grown in phase pure forms via hydrothermal reactions using SrCO3, Nb2O5, and an aqueous HF solution. Single-crystal X-ray diffraction suggests that Sr2Nb6O13F8·4H2O, crystallizing in the orthorhombic centrosymmetric space group, Pbam (No. 55), reveals a new variant of the three-dimensional tungsten bronze structure with three-, four-, and five-membered rings that are composed of corner-sharing NbO2(O/F)2F2, NbO4(O/F)F, NbO3(O/F)3, and SrO3F6 groups. Sr3Nb2O2F12·2H2O with the noncentrosymmetric polar space group, Cmc21 (No. 36), however, reveals a molecular structure consisting of Nb(O/F)2F5 pentagonal bipyramids and two unique Sr2+ cations interacting with F, O/F, and water molecules. Band gaps calculated by the Kubelka-Munk function based on the ultraviolet-visible diffuse-reflectance spectra of Sr2Nb6O13F8·4H2O and Sr3Nb2O2F12·2H2O are estimated to be ca. 3.22 and 4.11 eV, respectively, in which the values are related to the contents of electronegative F atoms and the Nb-O(F)-Nb bond angles influenced by structural distortion. An interesting phase transition reaction from Sr3Nb2O2F12·2H2O to thermodynamically more stable Sr2Nb6O13F8·4H2O occurs under a hydrothermal condition.

Two polymorphic phosphide-based infrared (IR) nonlinear optical (NLO) crystals, α-Ca2CdP2 and β-Ca2CdP2, were obtained by combining alkaline-earth metals and d10 transition metals using metal flux and metal salt flux methods, respectively. The crystal structure of α-Ca2CdP2 is orthorhombic in the space group Cmc21 (no. 36), while the structure of β-Ca2CdP2 is monoclinic in the space group Cm (no. 8). Both are two-dimensional layered structures that are composed of CdP4 tetrahedra layers via sharing vertices, which stack along the b-axis and the c-axis, respectively. The second harmonic generation (SHG) measurements manifest that α-Ca2CdP2 and β-Ca2CdP2 exhibit strong SHG intensities (1.41 and 3.28× that of AgGaS2 at a 2050 nm laser, respectively). Other optical measurements indicate that α-Ca2CdP2 and β-Ca2CdP2 have suitable band gaps (1.98 and 1.55 eV, respectively), high laser-induced damage thresholds (4.5 and 3.1× that of AgGaS2 at 1064 nm laser, respectively) and appropriate birefringence (0.12 and 0.20 at 2050 nm, respectively) in addition to covering wide infrared transparent regions. The research on α-Ca2CdP2 and β-Ca2CdP2 demonstrates that they are potential IR NLO candidates. Theoretical calculations uncover that their SHG effects are from distorted CdP4 tetrahedra, highlighting that tetrahedral motifs, including d10 transition metals, would be ideal NLO-active building blocks.

Diamond-like (DL) chalcophosphates, which possess the merits of impressive second-harmonic-generation (SHG) responses, strong laser-induced damage thresholds, and low melting points, are highly desirable for IR nonlinear-optical (NLO) applications. Herein, a new quaternary DL chalcophosphate, Cu5Zn0.5P2S8, is successfully discovered, taking known Cu3PS4 as the template via a single-site aliovalent-substitution strategy. It crystallizes in the orthorhombic system with noncentrosymmetric space group Pmn21, and the 3D DL structure is built by corner-shared [(Cu/Zn)S4], [CuS4], and [PS4] tetrahedra. Compared with its parent Cu3PS4, Cu5Zn0.5P2S8 exhibits a good phase-matching capability and a sharply enhanced SHG effect (10Cu3PS4) benefiting from partial Zn substitution. Moreover, the structure-performance relationships have been illustrated by means of theoretical investigations. Such an aliovalent-substitution strategy based on known DL semiconductors might be widely applied for the discovery of high-performance IR NLO crystals.

In this work, we report the synthesis as well as the structural and magnetic characterization of the three perovskites La2MnB'O6 (B' = Ti, Zr, and Hf). Interestingly, only La2MnTiO6 crystallizes in the monoclinic double perovskite space group P21/n, with a complete rocksalt order of the B-site cations, whereas La2MnZrO6 and La2MnHfO6 crystallize in the orthorhombic simple perovskite space group Pbnm, with complete disorder in the B site. Moreover, the magnetic susceptibility at low temperatures shows clear antiferromagnetic transitions below 10 K for the three compounds, but only the Ti-based perovskite has long-range magnetic ordering. The latter compound has an antiferromagnetic type-II structure described by the PS-1 magnetic space group, while the other two have a spin-glass behavior below the transition temperature due to both spin disorder and competing superexchange interactions in the systems. This is the first time that two of the three studied compounds were synthesized (B' = Zr and Hf) and the first time that the whole series is described in thorough detail using symmetry-adapted refinements and magnetic crystallography.

Inorganic chalcohalides are attracting a tremendous amount of attention because of their remarkable structural variety and desirable physical properties. Although great advances have been made in recent years, functional inorganic chalcohalides with two-dimensional neutral layers are still rare. Herein, two novel chalcohalides CdSnSX2 (X = Cl or Br) with high yields were obtained by reacting CdX2 with SnS using a traditional solid-state method at 823 K. Both of these chalcohalides adopt orthorhombic space group Cmcm (No. 63) with the following structural values: a = 4.014(4)-4.064(2) A, b = 12.996(2)-13.746(3) A, c = 9.471(2)-9.621(2) A, V = 494.1(8)-537.5(2) A3, and Z = 4. The prominent architectural feature is the unique two-dimensional [CdSnSX2] neutral layer consisting of composite [CdX2] and [SnS] sublattices that are connected alternately through the Cd-S-Sn bonds along the ac plane. The [CdX2] sublattice consists of a single octahedral chain of Cd-centered [CdX4S2] groups sharing cis-X edges, while the [SnS] sublattice consists of a bend-shaped chain of unusual [SnS2X2] units sharing vertices of S atoms. Significantly, each CdSnSX2 form (X = Cl or Br) shows high visible-light-induced photocatalytic activity for rhodamine B degradation, which is ∼7.0 times higher than that of nitrogen-doped TiO2 (TiO2-xNx) under the same experimental conditions. This discovery enriches the categories of inorganic chalcohalides and provides more choices of candidate materials for photocatalytic applications.

Mayenite Ca12Al14O33, as an oxide-ion conductor, has the potential of being applied in many fields, such as solid-oxide fuel cells. However, its relatively low oxide-ion conductivity hinders its wide practical applications and thus needs to be further optimized. Herein, a new recently developed glass crystallization route was used to prepare a series of Ga-doped Ca12Al14-xGaxO33 (0 ≤ x ≤ 14) materials, which is not accessible by the traditional solid-state reaction method. Phase evolution with the content of gallium, the corresponding structures, and their electrical properties were studied in detail. The X-ray diffraction data revealed that a pure mayenite phase can be obtained for 0 ≤ x ≤ 7, whereas when x > 7, the samples crystallize into a melilite-like orthorhombic Ca5Ga6O14-based phase. The electrical conduction studies evidence no apparent enhancement in the total conductivity for compositions 0 ≤ x ≤ 7 with the mayenite phase, and therefore, the rigidity of the framework cations and the width of the windows between cages are not key factors for oxide-ion conductivity in mayenite Ca12Al14O33-based materials, and changing the free oxygen content through aliovalent cation substitution may be the right direction. For compositions with a pure melilite-like orthorhombic phase, the conductivities also mirrored each other and are all slightly higher than those of the mayenite phases. These melilite-like Ca5Ga6O14-based materials show mixed Ca-ion, oxide-ion, and electron conduction. Furthermore, the conduction mechanisms of Ca ions and oxide ions in this composition were studied by a bond-valence-based method. The results suggested that Ca-ion conduction is mainly due to the severely underbonded Ca3 ions and that the oxide ions are most likely transported via oxygen vacancies.

Halides are one type of important IR nonlinear-optical material candidate. Here, a mixed alkali metal and d0 transition-metal fluoride, namely, KNa2ZrF7, was obtained by a facile hydrothermal method. It crystallizes in an orthorhombic system with the polar space group Pmn21, and its pseudo-1D structure features isolated (ZrF7)3- moncocapped trigonal prisms, which are ionically linked together by countercations K+ and Na+, representing a new type of fluoride. The powder sample of KNa2ZrF7 exhibits a moderate second-harmonic-generation response and a high laser-induced damage threshold. Besides, it can realize phase matchability and possesses a wide-IR transparent window. Thermal stability analysis suggests that KNa2ZrF7 is a congruent compound. Structural comparisons with related fluorides and theoretical calculations are also presented in this work.

The one-dimensional (1D) ABX3-type perovskite [(CH3)3PCH2F]CdCl2Br (1) has been obtained on the basis of the design of an organic-inorganic hybrid. Strikingly, it experiences sequential phase transitions at around 295 and 336 K, respectively. Given the noticeable steplike dielectric anomalies in the vicinity of 295 K, 1 is identified as a promising dielectric-switchable material. According to the single-crystal structure analysis, the order-to-disorder transformation of the [(CH3)3PCH2F]+ cation is the main reason for the phase transitions and the change of space group from the orthorhombic Pnma (No. 62) to the hexagonal P63/m (No. 176). This design of a perovskite structure will inspire more advances in the ever-growing field of switchable functional materials.

The present work is dedicated to characterization of the structural phase transition and incommensurate magnetic structure of the [CH3NH3][Ni(COOH)3] (1) perovskite-like metal-organic compound. The structural and magnetic characterization has been performed through variable-temperature single-crystal and powder neutron diffraction. Compound 1 crystallizes in the orthorhombic Pnma space group at room temperature. Below 84 K, a new phase has been observed. The occurrence of new reflections, which can be indexed with a wavevector along the c axis [q = 0.1426(2)c*], suggests the occurrence of an incommensurately modulated crystal structure. The structure was determined using the superspace group formalism on the Pnma(00γ)0s0 space group. This incommensurate phase remains unchanged with a decrease of the temperature up to the base temperature (ca. 2 K). Moreover, the magnetic susceptibility data, collected under zero-field-cooled and field-cooled conditions at different applied magnetic fields, show that compound 1 exhibits antiferromagnetic behavior below 34 K. In the current paper, we have confirmed that compound 1 presents the coexistence of nuclear and proper magnetic incommensurability below TN.

A new monoclinic α-polymorph of the Na2FePO4F fluoride-phosphate has been directly synthesized via a hydrothermal method for application in metal-ion batteries. The crystal structure of the as-prepared α-Na2FePO4F studied with powder X-ray and neutron diffraction (P21/c, a = 13.6753(10) A, b = 5.2503(2) A, c = 13.7202(8) A, β = 120.230(4)°) demonstrates strong antisite disorder between the Na and Fe atoms. As revealed with DFT-based calculations, α-Na2FePO4F has low migration barriers for Na+ along the main pathway parallel to the b axis, and an additional diffusion bypass allowing the Na+ cations to go around the Na/Fe antisite defects. These results corroborate with the extremely high experimental Na-ion diffusion coefficient of (1-5)·10-11 cm2·s-1, which is 2 orders of magnitude higher than that for the orthorhombic β-polymorph ((5-10)·10-13 cm2·s-1). Being tested as a cathode material in Na- and Li-ion battery cells, monoclinic α-Na2FePO4F exhibits a reversible specific capacity of 90 and 80 mAh g-1, respectively.

Four 3d-4f hetero-polymetallic complexes [Fe2Ln2((OCH2)3CR)2(O2CtBu)6(H2O)4] (where Ln = La (1 and 2) and Gd (3 and 4); and R = Me (1 and 3) and Et (2 and 4)) are synthesized and analyzed using elemental analysis, Fourier transform infrared spectroscopy, thermogravimetric analysis, and SQUID magnetometry. Crystal structures are obtained for both methyl derivatives and show that the complexes are isostructural and adopt a defective dicubane topology. The four heavy metals are connected with two alkoxide bridges. These four precursors are used as single-source precursors to prepare rare-earth orthoferrite pervoskites of the form LnFeO3. Thermal decomposition in a ceramic boat in a tube furnace gives orthorhombic LnFeO3 powders using optimized temperatures and decomposition times: LaFeO3 formed at 650 °C over 30 min, whereas GdFeO3 formed at 750 °C over 18 h. These materials are structurally characterized using powder X-ray diffraction, Raman spectroscopy, scanning electron microscopy, energy-dispersive X-ray map spectroscopy, and SQUID magnetometry. EDX spectroscopy mapping reveals a homogeneous spatial distribution of elements for all four materials consistent with LnFeO3. Magnetic measurements on complexes 1-4 confirm the presence of weak antiferromagnetic coupling between the central Fe(III) ions of the clusters and negligible ferromagnetic interaction with peripheral Gd(III) ions in 3 and 4. Zero-field-cooled and field-cooled measurements of magnetization of LaFeO3 and GdFeO3 in the solid-state suggest that both materials are ferromagnetic, and both materials show open magnetic hysteresis loops at 5 and 300 K, with Msat higher than previously reported for these nanomaterials. We conclude that this is a new and facile low temperature route to these important magnetic materials that is potentially universal, limited only by what metals can be programmed into the precursor complexes.

Black phosphorus (BP) allotrope has an orthorhombic crystal structure with a narrow bandgap of 0.35 eV. This material is promising for 2D technology since it can be exfoliated down to one single layer: the well-known phosphorene. In this work, bulk BP was synthesized under high-pressure conditions at high temperatures. A detailed structural investigation using neutron and synchrotron X-ray diffraction revealed the occurrence of anisotropic strain effects on the BP lattice; the combination of both sets of diffraction data allowed visualization of the lone electron pair 3s2. Temperature-dependent neutron diffraction data collected at low temperature showed that the a axis (zigzag) exhibits a quasi-temperature-independent thermal expansion in the temperature interval from 20 up to 150 K. These results may be a key to address the anomalous behavior in electrical resistivity near 150 K. Thermoelectric properties were also provided; low thermal conductivity from 14 down to 6 Wm-1K-1 in the range 323-673 K was recorded in our polycrystalline BP, which is below the reported values for single-crystals in literature.

Solid solutions Rb0.95NbxMo2-xO6.475-0.5x (x = 1.31-1.625) having a β-pyrochlore structure with an orthorhombic system were synthesized by solid-state reaction. The elemental composition was confirmed by X-ray microanalysis. The Rb0.95Nb1.375Mo0.625O5.79 structure refinement was performed using the Rietveld method. The crystal structure consists of ordered O-Mo-O chains partly occupied by Nb atoms. The oxygen vacancies are necessary to save the electroneutrality of the unit cell. It predominantly appears between Mo atoms that lead to form two disconnected defect octahedra [MoO5□···MoO5□]. The structural defects cause the low thermal stability; the compounds obtained decompose in the 748-758 °C temperature range. The high-temperature phase transition of the CsNbMoO6 and CsTaMoO6 nonlinear optical β-pyrochlores has been studied by differential thermal analysis, differential scanning calorimetric analysis, high-temperature X-ray diffraction analysis, and second harmonic generation analysis. At room temperature the compounds possess the cubic noncentrosymmetric F43m cell. Under heating to 437 °C and 401 °C for CsNbMoO6 and CsTaMoO6, respectively, they undergo transition into centrosymmetric Fd3m modification. This is accompanied by the SHG signal disappearing, as well as the 402 reflection, which is characteristic of the F43m space group. The positions of the valence and conduction bands were determined by reflectance spectra and XPS analysis for structure-related β-pyrochlores CsNbMoO6, CsTaMoO6, and Rb0.95Nb1.375Mo0.625O5.79.

The new binary chromium sulfide CrS3 has been synthesized by reaction of Cr3S4 and sulfur mixtures at 800 °C and 13 GPa. CrS3 crystallizes in an orthorhombic unit cell with a = 4.6742(7) A, b = 5.7...

In the synthesis of complex oxides, solid-state metathesis provides low-temperature reactions where product selectivity can be achieved through simple changes in precursor composition. The influence of precursor structure, however, is less understood in solid-state synthesis. Here we present the ternary metathesis reaction (LiMnO2 + YOCl → YMnO3 + LiCl) to target two yttrium manganese oxide products, hexagonal and orthorhombic YMnO3, when starting from three different LiMnO2 precursors. Using temperature-dependent synchrotron X-ray and neutron diffraction, we identify the relevant intermediates and temperature regimes of reactions along the pathway to YMnO3. Manganese-containing intermediates undergo a charge disproportionation into a reduced Mn(II,III) tetragonal spinel and oxidized Mn(III,IV) cubic spinel, which lead to hexagonal and orthorhombic YMnO3, respectively. Density functional theory calculations confirm that the presence of Mn(IV) caused by a small concentration of cation vacancies (∼2.2%) in YMnO3 stabilizes the orthorhombic polymorph over the hexagonal. Reactions over the course of 2 weeks yield o-YMnO3 as the majority product at temperatures below 600 °C, which supports an equilibration of cation defects over time. Controlling the composition and structure of these defect-accommodating intermediates provides new strategies for selective synthesis of complex oxides at low temperatures.

In this study, we succeeded in synthesizing new antiperovskite phosphides MPd3P (M = Ca, Sr, Ba) and discovered the appearance of a superconducting phase (0.17 ≤ x ≤ 0.55) in a solid solution (Ca1-xSrx)Pd3P. Three perovskite-related crystal structures were identified in (Ca1-xSrx)Pd3P, and a phase diagram was built on the basis of experimental results. The first phase transition from centrosymmetric (Pnma) to noncentrosymmetric orthorhombic (Aba2) occurred in CaPd3P near room temperature. The phase transition temperature decreased as Ca2+ was replaced with a larger-sized isovalent Sr2+. Bulk superconductivity at a critical temperature (Tc) of approximately 3.5 K was observed in a range of x = 0.17-0.55; this was associated with the centrosymmetric orthorhombic phase. Thereafter, a noncentrosymmetric tetragonal phase (I41md) remained stable for 0.6 ≤ x ≤ 1.0, and superconductivity was significantly suppressed as samples with x = 0.75 and 1.0 showed Tc values as low as 0.32 K and 57 mK, respectively. For further substitution with a larger-sized isovalent Ba2+, namely, (Sr1-yBay)Pd3P, the tetragonal phase continued throughout the composition range. BaPd3P no longer showed superconductivity down to 20 mK. Since the inversion symmetry of structure and superconductivity can be precisely controlled in (Ca1-xSrx)Pd3P, this material may offer a unique opportunity to study the relationship between inversion symmetry and superconductivity.

This work is focused on the structural and physical properties of CePt2Al2, an intermetallic compound. At room temperature, the modulated orthorhombic structure Cmme(a00)000, with q→= (0.481, 0, 0)...

Tungsten ditelluride (WTe2) is provoking immense interest because of its unique electronic properties, but studies about its semiconducting hexagonal (2H) phase are quite rare. Herein, we report the synthesis of semiconducting 2H WTe2 nanosheets with large positive magnetoresistance, for the first time, by a simple lithium-intercalation-assisted exfoliation strategy. Systematic characterizations including high-resolution transmission electron microscopy, X-ray diffraction, and Raman and X-ray photoelectron spectroscopies provide clear evidence to distinguish the structure of 2H WTe2 nanosheets from the orthorhombic (Td) phase bulk counterpart. The corresponding electronic phase transition from metal to semiconductor is also confirmed by density of states calculation, optical absorption, and electrical transport property measurements. Besides, the 2H WTe2 nanosheets exhibit large positive magnetoresistance with values of up to 29.5% (10 K) and 16.2% (300 K) at 9 T. Overall, these findings open up a promising avenue into the exploration of WTe2-based materials in the semiconductor field.

The oxyhalide-based solid electrolyte Li2OHCl usually forms the thermodynamically stable orthorhombic phase at room temperature and shows poor lithium ionic conductivity. Above 35 °C, a structural ...

The potential of the perovskite system Nd1-xSrxCoO3-δ (x = 1/3 and 2/3) as cathode material for solid oxide fuel cells (SOFCs) has been investigated via detailed structural, electrical, and electrochemical characterization. The average structure of x = 1/3 is orthorhombic with a complex microstructure consisting of intergrown, adjacent, perpendicularly oriented domains. This orthorhombic symmetry remains throughout the temperature range 373-1073 K, as observed by neutron powder diffraction. A higher Sr content of x = 2/3 leads to stabilization of the cubic perovskite with a homogeneous microstructure and with a higher oxygen vacancy content and cobalt oxidation state than the orthorhombic phase at SOFC operation temperature. Both materials are p-type electronic conductors with high total conductivities of 690 and 1675 S·cm-1 at 473 K in air for x = 1/3 and 2/3, respectively. Under working conditions, both compounds exhibit similar electronic conductivities, since x = 2/3 loses more oxygen on heating than x = 1/3, associated with a greater loss of p-type charger carriers. However, composite cathodes prepared with Nd1/3Sr2/3CoO3-δ and Ce0.8Gd0.2O2-δ present lower ASR values (0.10 Ω·cm2 at 973 K in air) than composites prepared with Nd2/3Sr1/3CoO3-δ and Ce0.8Gd0.2O2-δ (0.34 Ω·cm2). The high activity for the oxygen electrochemical reaction at intermediate temperatures is likely attributable to a large disordered oxygen-vacancy concentration, resulting in a very promising SOFC cathode for real devices.

The quaternary rare-earth-metal hafnium copper arsenides REHfCu2+δAs3 (where RE = La-Nd; δ ≈ 0.17) were obtained by direct reactions of the elements at 1073 K. They adopt a noncentrosymmetric orthorhombic crystal structure (space group Pmn21; a = 397.73(3)-392.37(2) pm, b = 1062.68(8)-1055.23(6) pm, c = 1307.25(9)-1291.40(7) pm for RE = La-Nd), which can be considered to be a Cu-deficient superstructure of the ternary Zr2Ni3P3-type structure found among metal-rich pnictides with a metal-to-nonmetal ratio close or equal to 2:1. The RE atoms occupy trigonal prismatic (CN6) and monocapped trigonal prismatic (CN7) sites, the latter resulting from the occurrence of Cu vacancies, the Hf atoms occupy octahedral sites (CN6), and the Cu atoms occupy tetrahedral sites (CN4). Band structure calculations on idealized models LaHfCu2As3 and LaHfCu2.5As3 suggest that the bonding situation improves by fractional occupation of the Cu3 site via depopulation of antibonding Cu-As states.

Among the KCoO2-type phases, the orthorhombic layered nitride CaTiN2 is a newly reported high dielectric permittivity material (er ∼ 1300-2500 within 104-106 Hz from 80 to 450 K) while the tetragonal SrTiN2 is reported to display an unintentional metallic conduction property. In this work, a Ca1-xSrxTiN2 solid solution was synthesized, in which the insulating SrTiN2 end member and some Sr-doped CaTiN2 samples were successfully obtained, and therefore, the dielectric properties of the Ca1-xSrxTiN2 solid solution were investigated. The Sr substitution for Ca drove an orthorhombic-to-tetragonal phase transformation in Ca1-xSrxTiN2, which reduced the dielectric permittivity significantly. The tetragonal SrTiN2 displays a much lower dielectric permittivity (er ∼ 20-70 in 105-106 Hz and 10-300 K) than that of CaTiN2. The comparison on the dielectric permittivities and structures of CaTiN2 and SrTiN2 indicates that the structural distortion arising from the splitting of N planes between Ti layers within the TiN2 pyramidal layers could be a plausible structural origin of the high bulk dielectric permittivity of CaTiN2.

Sr5Ga8O3S14, which is a novel nonlinear optical oxysulfide, was discovered via solid-state reaction. The compound crystallizes in noncentrosymmetric space group P21212 (No. 18) of the orthorhombic ...

Two polymorphs of a new cesium ferrogermanate zeotype, CsFeGeO4, were synthesized using the molten CsCl-CsF flux growth approach at 900 °C. The orthorhombic polymorph, referred to as (1), crystalli...

A novel niobium nitride, U2S3-type Nb2N3, has been successfully synthesized by nitridation of δ-NbN above approximately 30 GPa in a laser-heated diamond anvil cell. Nb2N3 crystallizes in the same orthorhombic structure (space group: Pnma) as η-Ta2N3. Nb2N3 consists of regular-shaped polyhedra, and the bulk modulus has been determined to K0 = 300(2) GPa. The low-temperature X-ray diffraction measurements have been successfully conducted for the tiny novel Nb2N3 between 297.7(5) and 106.3(3) K under ambient pressure. Nb2N3 shows no structural phase transition down to 106.3(3) K, and investigation of the linear thermal expansion coefficients yields αa = 3.36(9) × 10-6 K-1, αb = 5.39(10) × 10-6 K-1, αc = 6.77(15) × 10-6 K-1, respectively. Our study reveals that the incompressible novel nitride shows low thermal expansion behavior, which offers new insights for the development of functional nitrides and their crystal chemistry.

A new selenite-sulfate compound Co3(SeO3)(SO4)(OH)2 was prepared using a typical hydrothermal reaction. This compound is found to crystallize in an orthorhombic space group of Pnma, featuring a 2D ...

The recently discovered ferroelectricity in thin-film orthorhombic HfO2, which can be directly integrated into complementary metal–oxide semiconductor technology, has become an important research t...

Three new binary phases have been synthesized in the Ga-rich part of the Li-Ga system: LiGa6, Li11Ga24, and LiGa2. Their crystal structures and the respective phase formation conditions have been investigated with X-ray single crystal structure refinements, Rietveld refinements of X-ray powder diffraction data, and thermal analyses. They complete the Ga-rich part of the Li-Ga phase diagram together with the reported phases Li6-xGa14 with 2 ≤ x ≤ 3 and LiGa3.42. The compositions of two of the new gallides, LiGa6 and LiGa2, had been predicted in previous thermoanalytical studies, but their crystal structures remained unknown. All three new binary main group compounds adopt new structure types. LiGa6 crystallizes with the trigonal space group R3c (No. 167, a = 6.1851(8) A, c = 23.467(4) A), Li11Ga24 crystallizes with the hexagonal space group P63mc (No. 186, a = 13.7700(19) A, c = 23.250(5) A), and LiGa2 crystallizes with the orthorhombic space group Cmce (No. 64, a = 8.51953(4) A, b = 14.44163(7) A, c = 15.29226(7) A). All phases form air- and moisture-sensitive crystals of bright metallic luster. They can be synthesized starting from the pure elements and taking into account their incongruent melting behavior by adequate tempering sequences derived from differential scanning calorimetry (DSC) studies of the system. Lithium gallides do not form electron-precise Zintl phases. The electronic structures of these polar intermetallic phases combine ionic, covalent, and metallic bonding contributions and have been analyzed by density functional theory (DFT) calculations in the cases of LiGa6 and LiGa2. Measurements of the specific electronic resistivities have also been performed and prove the metallic behavior.

Ba10Fe3Sb7Se24 was synthesized using a KBr flux at 850 °C (Crystal Data: orthorhombic, Cmc21, a = 9.3412(2) A, b = 44.6666(10) A, c = 12.5496(3) A, V = 5236.2(2) A3, and Z = 4). The compound adopts a new three-dimensional framework constructed by the layer to include Fe2Se6 dimers and FeSe4 tetrahedra in the linkage motifs of [Fe2SbSe10] and [FeSb6Se14], respectively. Alternatively, the all Sb-based polyhedra are assembled as a semiconducting, perovskite-like framework lacking an inversion center where these Fe-based magnetic units are trapped within the interstices. The strong antiferromagnetic interaction is revealed by a high Curie constant of -113 K, but the curvature of field-cooled and zero-field-cooled magnetic susceptibilities bifurcating at ∼19 K is observed. The critical temperature is well verified by a broad peak of χM″ signal showing a rapid increase below 19 K under an alternating current field. The Fe2Se6 dimer featuring distorted edge-sharing tetrahedra to induce the spin-canted antiferromagnetic ordering strongly dominates such magnetic ordering. Finally, a weak hysteresis loop is clearly observed at 2.0 K. This dilute magnetic selenide displays a direct bandgap at ∼1.54 eV, analyzed by the Tauc equation. Interestingly, the use of second-harmonic-generation temperature dependence shows a turning point at ∼20 ± 1 K, which precisely corresponds to the magnetic ordering temperature within the error bar, thereby demonstrating the versatility of the technique for probing magnetic phase transition.

Four types of bismuth oxides, Na3Bi3O8, NaBiO3, α-Bi2O3, and e-Bi2O3, were obtained by hydrothermal reactions using NaBiO3·nH2O in NaOH solution. The crystal structure of a new phase (Na3 Bi3+)Bi25+O8 ((Na0.75Bi0.25)2BiO4) was determined by using single crystal X-ray diffraction data, and this compound was found to show a Na2MnCl4-related structure with a monoclinic system (space group, Pm) with the following lattice parameters: a = 5.990 (2) A, b = 3.335 (2) A, c = 10.108 (2) A, and β = 91.08 (3)°. The final R-factors R1 and wR2 were 0.041 and 0.090 (all data), respectively. The new phase was composed of mixed valence states of Bi (Bi3+ and Bi5+, with a mean Bi valence of 4.30) with five distinct Bi sites, where two Bi5+ (Bi1 and Bi2) fully occupied the distorted octahedral sites and three Bi3+ (Bi3, Bi4, and Bi5) were statistically distributed at the split sites with Na+ (Na3, Na4, and Na5). The Na6 site is fully occupied. The distorted Bi5+O6 octahedra formed one-dimensional chains via edge-sharing along the b-axis, with the chains held by Bi3+/Na+ split sites. The structural feature except for the split distribution of Bi3+/Na+ was classified as a Na2MnCl4-type structure. DFT calculations based on a model discounting the split distribution of Bi3+/Na+ indicated that Bi 6s and O 2p orbitals form sp hybridization at the conduction band. This new mixed valence bismuth oxide exhibited photocatalytic activity for phenol degradation under visible light irradiation. In addition to Na3Bi3O8, the hydrothermal reaction using NaBiO3·nH2O in NaOH solution yielded micrometer-sized single crystals of an ilmenite-type NaBiO3 and two polymorphs of bismuth oxides with monoclinic (α-Bi2O3) and orthorhombic (e-Bi2O3) structures, depending on the reaction temperature and NaOH concentration.

Commercial white LED devices usually suffer from a high color temperature and poor color rendering. Developing a new, efficient, and stable red phosphor is the key to solving this problem. In this work, a series of pure Ca3Y2-xB4O12:xEu3+ (0 < x ≤ 2) samples, including the new and fully transitional borate phosphor Ca3Eu2B4O12 (CEBO), have been successfully prepared by solid-state reaction synthesis. CEBO is isostructural with Ca3Y2B4O12 (CYBO), belonging to the orthorhombic system with space group Pnma (No. 62). Under optimal 393 nm excitation, this borate exhibits a strong red emission, peaking at 615 nm, with high color purity. Interestingly, the luminescence of CEBO is relatively higher than that of CYBO:Eu3+ phosphors. The quantum yield of this non-concentration-quenching phosphor reaches 95.6%. Furthermore, a warm pc-WLED device has been fabricated by mixing as-prepared CEBO powders and commercial BaMgAl10O17:Eu2+ and (Sr, Ba)2SiO4:Eu2+ phosphors, which exhibits a high color rendering index (Ra = 83.7) along with a color temperature of around 3883 K. The present work indicates that this new borate, with outstanding quantum efficiency and favorable thermal stability, can be used as a red phosphor for application in WLEDs.